(1) Field of the Invention
The present invention relates to the technical field of inlet barrier filters on engines or on auxiliary power units with radial air intake. Aircrafts or helicopters often have engines, for example turbo-shaft engines with a ring-shaped inlet barrier filter surrounding and covering a radial air intake.
(2) Description of Related Art
These filters, which are exposed to many different operating and background conditions, in particular in aircrafts, can be clogged after some time of operation of the barrier filter. The power provided by the engine will then fall down, what could lead to a stall of the aircraft. In such a situation, the safety of the aircraft is no more guaranteed.
It is the reason why in the past, the inlet barrier filters on engines with radial air intake, were installed on the fuselage or in an air intake channel of the vehicle and not directly on the radial air intake of the engine. It was known to integrate a bypass system in such a channel, which would feed the engine with air in case that a clogging of the barrier filters occurs.
The ring-shaped filters were used only on auxiliary power units with radial air intake, since it was not possible to integrate a bypass system on a radial air intake and since a clogging of the barrier filter on the auxiliary power unit was not critical with respect to the safety of the aircraft.
Integrating a bypass system in an air intake channel is associated with disadvantages when used in aircraft, in particular in helicopters, because both, the channel and the bypass system should be as compact as possible in order to reduce as much as possible their space requirement. This can very easily lead to an increase in conception, manufacturing and fabrication costs.
Another disadvantage arises because retrofitting a filter with a bypass system on a fuselage or in an air intake channel of an existing helicopter or aircraft, is a big change on the air intake and usually causes a lot of qualification and certification work.
It is also known, for example with document FR 2 906 569 to provide an aircraft with a polyvalent air inlet for a turbo-shaft engine, which has a movable closing unit for closing a non filtering air inlet when the aircraft is at proximity of the ground and closing a filtering inlet during flying of the aircraft. The closing unit is a cylindrical and movable tube with an opening which is set either facing the filtering inlet or facing the non filtering inlet.
It is also known, for example with document FR 2 924 471 to provide an aircraft with an air intake for a turbo-shaft engine equipped with a controlled filtering system. The filtering means are compressed within a corresponding frame in order to open the radial air intake at several positions for direct air admission without filtering.
It is the object of the invention to overcome the mentioned disadvantages and to be able to provide a filtering device for engines or power units with radial air intake, which integrates a bypass system and which is located on the radial air intake.
It is an additional object of the invention to provide a filtering device for engines or power units with radial air intake, which needs a low space requirement in the aircraft.
It is an additional object of the invention to provide a filtering device for engines or power units with radial air intake, which has a low number of parts, which is cheap, easy to manufacture and to replace.